Hi,
I'm afraid that not possible :
The vendor data is stored directly in the database and a lot of actions are made without session or else.
If you want vendors with different emails, you need to create several vendors.
But because you can send an email to the vendor with any kind of context, what you want to do is not possible.
Thanks to custom development you should be able to do a lot of things ; probably what you want to achieve but the way that you want to achieve that (using the session) is not the right one and will not work at all.
Regards,